The 70 KDA Heat Shock Protein Hsp70 as Part of a Protein Disaggregase System

Proteins participate in a wide variety of cellular functions, which enable many activities in our body. However, proteins need to reach their correct state of folding to function properly. In the cell, the folding of many nascent proteins is aided by the 70 kDa heat shock protein (Hsp70). When folding is not favorable, misfolded species accumulate leading to the formation of aggregates, which leads to loss of function and is the basis of several diseases. In addition to its function of aiding folding, Hsp70 is also an important agent in disaggregation, sometimes acting in a bichaperone system together with Hsp100 in several organisms, such as bacteria, fungi and plants. Surprisingly, animals lack a bonafide Hsp100 orthologue. To overcome this limitation, animals evolved a Hsp70-based disaggregation system, in which Hsp70 cooperates with Hsp40 and Hsp110 co-chaperones to reactivate aggregated substrates. This chapter revises the most recent models for the mechanism of interaction between these proteins and how they cooperate to solubilize protein aggregates.